We stick with Graphalloy for high temp pumps of all types, including many BFW pumps. The material matches housing thermal expansion and has a much larger temp range than Vespel or other plastics. It also ends up being less expensive.
why not check out www.graphalloy.com for bushings and bearings? Graphalloy is a graphite metal alloy and they have many years of successful experience in BFW pumps. The material is non-galling, dry-running, dimensionally stable, and is also used for high-temp applications around 750F.